The audio filter on the A500 is not permanent. Sounds like you need to replace the electrolytics in your audio section.
You are right in saying the Amiga doesn't look the best on an LCD/Plasma. But surely you're using an LCD monitor on your PC? Either way, I'd strongly recommend using a CRT TV if you have one.
Emulators will never be able to reproduce the incredibly smooth scrolling of the Commodore machines. That to me is the main reason why the real thing will always be better.